Police Baffled? Send For The Radio Amateurs!

August 26, 2016 by Jenny List 88 Comments

The police force in Evanston, Illinois had a problem on their hands. A mystery transmitter was blocking legal use of radio devices, car key fobs, cellphones, and other transmitters in an area of their city, and since it was also blocking 911 calls they decided to investigate it. Their first call for help went to the FCC who weren’t much use, telling them to talk to the manufacturers of the devices affected.

Eventually they approached the ARRL, the USA’s national amateur radio organisation, who sent along [Kermit Carlson, W9XA] to investigate. He fairly quickly identified the frequencies with the strongest interference and the likely spot from which it originated, and after some investigation it was traced to a recently replaced neon sign power supply. Surprisingly the supply was not replaced with a fault-free unit, its owner merely agreeing to turn it off should any further interference be reported.

The ARRL are highlighting this otherwise fairly unremarkable case to draw attention to the problem of devices appearing on the market with little or no pretence of electromagnetic compatibility compliance. In particular they are critical of the FCC’s lacklustre enforcement response in cases like this one. It’s a significant problem worldwide as huge numbers of very cheap switch-mode mains power supplies have replaced transformers in mains power applications, and in any center of population its effects can be readily seen with an HF radio in the form of a significantly raised RF noise floor. Though we have reported before on the FCC’s investigation of the noise floor problem we’d be inclined to agree with the ARRL that it is effective enforcement of EMC regulations that is key to the solution.

City of Evanston police vehicle picture, [Inventorchris] (CC BY-NC 2.0) via Flickr.

A Refrigerator Cooled By Rubber Bands

August 25, 2016 by Adam Fabio 35 Comments

Ever noticed that a rubber band gets warmer when it’s stretched? The bands also get cooler when allowed to snap back to relaxed length? [Ben Krasnow] noticed, and he built a rubber band cooled refrigerator to demonstrate the concept. The idea of stretching a rubber band to make it hotter, then releasing it to make it cooler seems a bit counter intuitive. Normally when things get smaller (like a gas being compressed) they get hotter. When pressure is released the gas gets cooler. Rubber bands do the exact opposite. Stretching a rubber band makes it hot. Releasing the stretched band causes it to get cooler.

No, the second law of thermodynamics isn’t in jeopardy. The secret is in the molecular structure of rubber bands. The bands are made of long polymer chains. A relaxed rubber band’s chains are a tangled mess. Stretching the band causes the chains to untangle and line up in an orderly fashion. By stretching the band you are decreasing its entropy. The energy of the molecules in the band don’t change, but entropy does. All the work one does to stretch the band has to go somewhere, and that somewhere is heat. This is all an example of entropic force. For a physics model of what’s going on, check out ideal chains. If you’re confused, watch the video. [Ben] does a better job of explaining entropic force visually than we can with text.

To test this phenomenon out, [Ben] first built a wheel with rubber bands as spokes. Placing the wheel in front of a heater caused it to slowly rotate. [Ben] then reversed the process by building a refrigerator. He modeled his parts in solidworks, then cut parts with his Shaper handheld CNC. The fridge itself consists of an offset wheel of rubber bands. The bands are stretched outside the fridge, and released inside. Two fans help transfer the thermal energy from the bands to the air. The whole thing is hand cranked, so this would make a perfect museum or educational demonstration. Cranking the fridge for 5 minutes did get the air inside a couple of degrees cooler. Rubber is never going to displace standard refrigerants, but this is a great demo of the principles of entropic force.

For more thermodynamic fun, check out [Al Williams] recent article about building a DIY heat pipe.

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Arduino Versus Logic: The Coil Gun War Continues

August 25, 2016 by Dan Maloney 23 Comments

Looks like another shot has been fired in the simmering Coil Gun Control War. This time, [Great Scott] is taken to the discrete woodshed with a simplified and improved control circuit using a single CMOS chip and a few transistors. Where will it end? Won’t somebody think of the children?

The latest salvo is in response to [GreatScott]’s attempt to control a DIY coil gun with discrete logic, which in turn was a response to comments that he took the easy way out and used an Arduino in the original build. [Great Scott]’s second build was intended to justify the original design choice, and seemed to do a good job of explaining how much easier and better the build was with a microcontroller. Case closed, right?

Nope. Embedded designer [fede.tft] wasn’t sure the design was even close to optimized, so he got to work — on his vacation, no less!’ He trimmed the component count down to a single CMOS chip (a quad Schmitt trigger NAND), a couple of switching transistors, the MOSFETs that drive the coils, and a few passives. The NANDs are set up as flip-flops that are triggered and reset by the projectile sensors, which are implemented as hardwired AND gates. The total component count is actually less than the support components on the original Arduino build, and [fede.tft] goes so far as to offer ideas for an alternative that does away with the switching transistors.

Even though [fede.tft] admits that [GreatScott] has him beat since he actually built both his circuits, hats off to him for showing us what can likely be accomplished with just a few components. We’d like to see someone implement this design, and see just how simple it can get.

Fine Business, Good Buddy: Amateur Radio For Truckers

August 25, 2016 by Dan Maloney 51 Comments

Summer is the season for family road trips here in the US, and my family took to the open road in a big way this year. We pulled off a cross-country relocation, from Connecticut to Idaho. Five days on the road means a lot of pit stops, and we got to see a lot of truck stops and consequently, a lot of long-haul truckers. I got to thinking about their unique lifestyle and tried to imagine myself doing that job. I wondered what I’d do hour after long hour, alone in the cab of my truck. I figured that I’d probably just end up listening to a lot of audio books, but then I realized that there’s a perfect hobby for the road — ham radio. So I decided to see how ham radio is used by truckers, and mull over how a truck driver version of me might practice The World’s Best Hobby.

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Hands-On The Shaper Origin: A Tool That Changes How We Build

August 25, 2016 by Gerrit Coetzee 199 Comments

I bet the hand saw really changed some things. One day you’re hacking away at a log with an ax. It’s sweaty, awful work, and the results are never what you’d expect. The next day the clever new apprentice down at the blacksmith’s shop is demoing his beta of his new Saw invention and looking for testers, investors, and a girlfriend. From that day onward the work is never the same again. It’s not an incremental change, it’s a change. Pure and simple.

This is one of those moments. The world of tools is seeing a new change, and I think this is the first of many tools that will change the way we build.

Like most things that are a big change, the components to build them have been around for a while. In fact, most of the time, the actual object in question has existed in some form or another for years. Like a crack in a dam, eventually someone comes up with the variation on the idea that is just right. That actually does what everything else has been promising to do. It’s not new, but it’s the difference between crude and gasoline.

My poetic rasping aside, the Shaper Origin is the future of making things. It’s tempting to boil it down and say that it’s a CNC machine, or a router. It’s just, more than that. It makes us more. Suddenly complex cuts on any flat surface are easy. Really easy. There’s no endless hours with the bandsaw and sander. There’s no need for a 25,000 dollar gantry router to take up half a garage. No need for layout tools. No need to stress about alignment. There’s not even a real need to jump between the tool and a computer. It can be both the design tool and the production tool. It’s like a magic pencil that summons whatever it draws. But even I had to see it to believe it.

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Fail Of The Week: Machining Bismuth

August 24, 2016 by Jenny List 62 Comments

[David Cook]’s summary below the write-up of his experiences working with a bismuth ingot is succinct.

“I wasted a weekend learning why elemental bismuth is not commonly used for metal parts.“

It’s a fair assessment of his time spent growing unspectacular bismuth crystals, casting a bismuth cylinder that cracked, and machining bismuth only to be left with a very rough finish. But even though he admits the exercise was unsuccessful, he does provide us with a fascinating look at the physical properties of the element.

This is what [David] wanted to make. Alchemist-hp + Richard Bartz with focus stack. (Own work) [CC BY-SA 3.0], via Wikimedia Commons

Bismuth is one of those elements you pass by in your school chemistry lessons, it has applications in machining alloys and as a lead replacement but most of us have never knowingly encountered it in the real world. It’s one of the heavy metals, below antimony and to the right of lead on the Periodic Table. Curious schoolchildren may have heard that like water it expands on solidifying or that it is diamagnetic, and most of us have probably seen spectacular pictures of its crystals coated in colourful iridescent oxides.

It was a Hackaday story about these crystals that attracted [David] to the metal. It has a low enough melting point – 271.5 °C – that it can be liquified on a domestic stove, so mindful of his marital harmony should he destroy any kitchen appliances he bought a cheap electric ring from Amazon to go with his bismuth ingot. and set to work.

His first discovery was that cheap electric rings outdoors aren’t very effective metallurgy furnaces. Relocating to the kitchen and risking spousal wrath, he did eventually melt his bismuth and pick off the top layer once it had resolidified, to reveal some crystals.

Unfortunately for him, instead of spectacular colors and huge crystals, the sight that greeted him was one of little brilliance. Small grey crystals with no iridescence. It seems the beautiful samples are made by a very slow cooling of the liquid bismuth, followed by a quick pouring off of the remaining molten metal. Future efforts, he assures us, will involve sand-insulated molds and careful temperature monitoring.

Undeterred, he continued with his stock of bismuth and embarked on the creation of a cylinder. Early efforts with a clay mold resulted in cracked cylinders, so in desperation he cast the entirety of the metal in an aluminium baking tray and cut the resulting ingot to a rough piece of stock for turning.

With the bismuth in the lathe, he then came face to face with what he alluded to in his conclusion above, why machined bismuth parts aren’t something you’ll encounter. His cylinder came out with significantly rough patches on the surface, because bismuth is both crystalline and brittle. He suggests improvements could be made if the metal could be solidified with fewer crystals, but it’s obvious that elemental bismuth on its own is not a winner in the turning stakes.

We suggest you take a look at [David]’s write-up. It may be presented as a Fail of The Week here, but in fact it’s more of a succession of experiments that didn’t work than an unmitigated disaster. The result is an interesting and well-documented read that we’re sure most Hackaday readers will gain something from.

Aside from the bismuth crystals linked to above, we’ve featured bismuth a few times here at Hackaday. A low-temperature soldering process used it in an alloy, and we’ve even featured someone using it in another alloy to print using a RepRap.

Thanks [nebk] for the tip.

Tools Of The Trade – Test And Programming

August 24, 2016 by Bob Baddeley 15 Comments

In our final installment of Tools of the Trade (with respect to circuit board assembly), we’ll look at how the circuit board is tested and programmed. At this point in the process, the board has been fully assembled with both through hole and surface mount components, and it needs to be verified before shipping or putting it inside an enclosure. We may have already handled some of the verification step in an earlier episode on inspection of the board, but this step is testing the final PCB. Depending on scale, budget, and complexity, there are all kinds of ways to skin this cat.

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